JP2534105B2 - Solid-state imaging device and signal reading method thereof - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device and a signal reading method thereof, and more particularly to a solid-state imaging device using a vertical transfer line as a photosensitive area.

(Prior Art) Conventionally, for example, a frame transfer type solid-state imaging device is composed of a vertical CCD and a horizontal CCD that serve both as a photoelectric conversion and an analog shift register, and is sent from a light receiving unit during a vertical blanking period. After the signal charge for one screen is stored in the storage unit once, it is slowly sent to the horizontal CCD at the bottom row by row and read out sequentially.

In addition, as shown in FIG. 6, the interline transfer type solid-state imaging device includes a light receiving element 5 including a plurality of photodiodes and a vertical and horizontal shift register of a CCD.
7 and 8, the signal charge accumulated in the photodiode for one frame period is sent to the vertical CCD all at once by opening the transfer gate 6 during the vertical blanking period. After closing the transfer gate 6, the charges are sequentially transferred downward,
It is read at the output terminal 9 through the CCD.

Here, the surfaces of the transfer gate 6 and the shift registers 7 and 8 excluding the light receiving element are shielded by an aluminum film or the like (in the figure,
A shaded area) is provided so that noise components and the like due to external light do not mix with the signal charge.

(Problems to be Solved by the Invention) However, in these solid-state imaging devices, in the case of the frame transfer method, since the light receiving section has two functions of charge accumulation and transfer, an effective signal charge is obtained. It was difficult to increase the integration time, and it was difficult to improve the sensitivity.

In addition, since incident light is absorbed or reflected by the transfer electrode that constitutes the CCD, there is a problem that the photosensitivity is particularly low for short wavelength light.

On the other hand, in the case of the interline transfer method, as is clear from the figure, it is difficult to improve the light integration efficiency because a light-shielded shift register and the like are present in the light receiving section, and it is difficult to improve Since there is a light shielding film part in
There is a problem that the resolution in the horizontal direction decreases.

The present invention has been made in view of such circumstances,
It is an object of the present invention to provide a solid-state image pickup device having both improved sensitivity and resolution.

Another object of the present invention is to provide a signal reading method for reading the signal of such a solid-state image pickup device by a method suitable for digital recording.

(Means and Actions for Solving the Problems) That is, the above-mentioned object of the present invention is to provide a photosensitive region including at least a plurality of light-receiving elements, a vertical charge transfer section and a horizontal charge that are attached to each vertical column of the light-receiving element. The vertical charge transfer unit has a transfer unit, in which case the vertical charge transfer unit can not only transfer the charges formed in the light receiving element, but also perform photoelectric conversion by itself, and the vertical charge transfer unit can perform the photoelectric conversion.
A color filter that forms a signal of one color (for example, R) having a long wavelength of the primary color or the complementary color and forms signals of the remaining two colors (for example, G and B) in the light receiving element is arranged. This is achieved by a solid-state image pickup device having a feature.

In addition, another object of the present invention is to first form a signal charge, which is generated by exposing the solid-state imaging device for a predetermined period of time, first in a vertical charge transfer unit via a horizontal charge transfer unit.
Signal charge of the second color, the signal charge of the second color formed in the light receiving element next is transferred to the vertical charge transfer section, and the signal charge of the second color is received next through the horizontal charge transfer section. Solid-state imaging characterized in that the signal charges of the third color formed on the element are transferred to the vertical charge transfer section, and the signal charges of the third color are read out in the frame sequential manner through the horizontal charge transfer section. This is achieved by the signal reading method of the device.

Since the solid-state imaging device of the present invention does not have an optical shield in the vertical charge transfer section, it can also form an optical signal charge by itself. For example, a micro color filter is provided on the photosensitive area and the vertical charge transfer section, and each light receiving element in the photosensitive area is assigned to a color of B or G, and the vertical charge transfer section outputs an R color signal. Is configured to generate.

Then, the exposure time is regulated by the combined use of a mechanism and a shutter to form the signal charges of each color, and after closing the shutter, the signal charges of each color are taken out in a frame-sequential manner to obtain an output without color mixture.

(Example) Hereinafter, one example of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a solid-state imaging device according to the present invention, in which the light receiving portion 10 and the horizontal charge transfer portion 11 are shown as simplified individual blocks.

The light receiving unit 10 is attached to each of the photosensitive regions 14 formed by a group of light receiving elements formed of photoelectric conversion elements arranged in a vertical direction as shown by a dotted rectangle in FIG. A plurality of photosensitive regions formed from the vertical charge transfer unit 15.
The vertical charge transfer portions 15 and the vertical charge transfer portions 15 are alternately provided in the horizontal direction (the horizontal direction in the drawing).

On the surface of each light receiving element in the photosensitive region 14, blue filters and green filters indicated by symbols B and G are alternately provided in the vertical direction.

The vertical charge transfer portion 15 is composed of transfer elements arranged so as to correspond to each light receiving element of the photosensitive area 14 as shown by a dotted rectangle in the figure, and each transfer element has a photoelectric conversion function. , And has a function of transferring signal charges downward by mutual transfer operations. That is, the vertical charge transfer unit 15 is composed of a self-scanning image pickup device.

On the surface of the vertical charge transfer portion 15, a red filter indicated by the symbol R is provided in a stripe shape.

On the output side of the light receiving unit 10, a horizontal charge transfer unit 11 composed of a horizontal CCD that transfers the signal charge in the horizontal direction via a transfer gate Tg is arranged, and the signal charge transferred to the horizontal charge transfer unit 11 is output. It is read from the output terminal 13 through the amplifier 12.

 Next, the configuration of the light receiving unit 10 will be described with reference to FIG.

The vertical charge transfer section 15 under the filter R is provided with a plurality of polysilicon transfer electrodes 18 and 19 extending in the horizontal direction and is driven by two-phase driving (φV _{1 to} φV ₂ ) to lower the charge. Transfer sequentially. On the other hand, filters G and B in the photosensitive area 14
The surface of the light receiving element below is opened so that the transfer electrode 1
7,18 are not provided. Instead, a third thin polysilicon electrode 20 is provided on each photosensitive region 14 along the vertical direction.

Further, although not shown in the figure, a fixed potential barrier is formed between the light receiving element surrounded by the channel stopper indicated by the dotted line and the transfer element forming the vertical charge transfer unit 15. It is provided so that the generated signal charges are not transferred to the light receiving element.

That is, in the light receiving element and the transfer element in which the potential potential moves up and down with the potential barrier as a boundary, the light receiving element is provided deeper than the barrier because the voltage φp is applied by the third thin polysilicon electrode 20 during charge accumulation. The signal charges are stored therein, and are stored at a potential level higher than the barrier during field transfer to transfer the charges to the transfer element. On the other hand, the transfer element is provided so that the level does not become higher than the barrier even when the charge is transferred, which has a higher potential level than when the charge is stored.

Further, one of the features of the solid-state imaging device of the present invention is that a filter that forms a signal charge of long-wavelength light (color R) is arranged on the vertical charge transfer unit, and this long-wavelength optical signal charge is another. That is, the signal is read first before the optical signal charge of the wavelength.

This is because the long-wavelength optical signal charge has large leakage of light and diffusion of carriers generated in the deep portion of the substrate, and has a great influence on other light receiving elements.

In the solid-state imaging device of the present invention configured as described above, the filter is also arranged in the transfer section and the light-shielding film is removed. Then, it is necessary to limit the exposure period by the shutter and transfer the charges after the exposure is completed.

FIG. 3 shows a charge reading sequence when the solid-state imaging device of the present invention is applied to an electronic still camera.

In the solid-state imaging device, in the unexposed state immediately before the shutter is opened, the sweeping operation of the dark current generated under each color filter is performed all at once. Then, the shutter is opened to perform exposure for a predetermined period. During this period, either one of the transfer electrodes 18 and 19 shown in FIG.
Is provided at a "High" level to which a voltage is applied to accumulate charges.

Either one of the transfer electrodes 18 and 19 is set to “H
By providing the electrode at the "igh" level and the other electrode at the "Low" level, the lower part of the "Low" level electrode acts as a potential barrier in the vertical direction.

When exposure is performed for a predetermined period of time and the shutter is closed, the read mode is set and the signal charges generated under the filter are read frame by frame for each color. Then, the device enters the next imaging mode again.

FIG. 4 shows the read timing in the read mode.

First, the charge of the R signal accumulated under the transfer electrode 18 (φV ₁ ) of the vertical charge transfer unit 15 is read. At that time, the electrode 20
(Φp) is maintained at “High” level,
The signal charges of G and B generated under 14 are left in the accumulation state as they are. Transfer electrodes 18 and 19 are driven alternately (φV _{1 to} φ
V ₂ ) and vertically transfer the charges downward, and send them to the horizontal CCD row by row from the output side. The horizontal CCD is driven in two phases (φH _{1 to} φH ₂ ) to transfer charges in the horizontal direction at high speed, and the output amplifier 12 reads out the signal charges for one row from the output terminal 13 in accordance with the read timing (φs). Then, the R signal generated in the vertical charge transfer unit 15 is completely read out in 1/60 seconds by repeating the above operation and stored in a frame memory or the like to form a frame image.

Next, in this embodiment, the signal charge corresponding to the B filter in the photosensitive area 14 is read out. Electrode 20 (φp) is "Low"
The transfer electrode 18 (φV ₁ ) on the transfer element corresponding to this light receiving element is set to “High”
When provided at the level, the charges are field-shifted from the photosensitive area 14 to the vertical charge transfer portion 15. The field-shifted signal charge is transferred to the transfer electrodes 18, 1 as in the case of the R signal.
The data is vertically transferred by 9 and further sequentially read from the output terminal 13 row by row through the horizontal CCD and the output amplifier. And
All the signal charges of color B are read out in 1/60 seconds.

When the reading of the signal charge of the color B is completed, the signal charge corresponding to the G filter of the photosensitive area 14 is finally read. That is, since the electrode 20 (φp) is provided at the “Low” level and the transfer electrode 19 (φV ₂ ) on the transfer element corresponding to the light receiving element of the G filter is provided at the “High” level, the signal charge is Vertical charge transfer unit
Field-shifted to 15. The signal charges of the color G field-shifted to the vertical charge transfer unit 15 are the same as the colors R and B described above.
The signal charges are vertically transferred by the transfer electrodes 18 and 19 in the same manner as the signal charges of, and all are read out in 1/60 seconds via the horizontal CCD.

FIG. 5 is a block diagram showing the concept of an electronic still camera to which the solid-state imaging device of the present invention is preferably applied.

In the figure, an image of a subject incident through an imaging optical system 21 and a shutter 22 is picked up by a solid-state image pickup device 24 of the present invention controlled by a drive IC 23, and is separated into three primary color components R, G, B. Image signals are output in a frame-sequential manner.

In the image signal output in the frame-sequential manner, the field signal of the first color (color R in this embodiment) is an analog signal processing circuit.
After being supplied to 25 and undergoing various signal processing, A / D conversion circuit 26
After being digitized by and further supplied to the digital signal processing circuit 27 and subjected to signal processing such as interpolation and band compression,
It is recorded on the memory card 28.

The analog signal processing circuit 25 is composed of a sample hold circuit 25a, an amplifier 25b, and a gamma correction circuit 25c, and the solid-state image pickup device 24 and each signal processing circuit, etc. are provided with a synchronization signal from a synchronization signal generator 29. Controlled.

Next, the field signal of the second color (color B) output from the solid-state imaging device 24 is similarly digitized and recorded in the memory card 28, and finally the third color (color G).
Field signals are recorded.

Then, the image signals of the three fields recorded on the memory card 28 are simultaneously read at the time of reproduction to form one color screen.

Although the R, G, B3 primary color filters are used in the above-mentioned embodiment, the present invention is not limited to this, and for example, Cy,
A complementary color system of Mg and Ye can also be used. At this time, a Cy filter is arranged on the vertical charge transfer unit.

Further, in the above-described embodiment, the case where the vertical charge transfer unit is driven in two phases is described, but it may be driven in three phases or four phases.

Furthermore, although the non-interlace method is described in the above-mentioned embodiment, the A field read every other row in the vertical direction as the interlace method and the signal of the B field similarly read every other row in the vertical direction. Still images can also be formed.

(Effects of the Invention) As described above, according to the solid-state imaging device of the present invention, since the vertical charge transfer unit also has the photoelectric conversion function, the number of light-receiving elements is increased and the resolution can be improved. Moreover, since the area where light can be received increases, the sensitivity can be increased. Further, since the image signals of the respective colors are output in the frame-sequential manner, all the signal processing systems in the subsequent stages can be made into one channel and the circuit scale can be reduced. In addition, since it is a frame-sequential output, real-time image processing for each color is easy,
The load on the A / D conversion circuit and other digital signal processing can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing the configuration of one embodiment of a solid-state image pickup device according to the present invention, FIG. 2 is a main part surface view showing the structure of the light receiving part of FIG. 1 from the surface, and FIG. 3 is the present invention. FIG. 4 is a timing diagram for explaining a signal read sequence of the solid-state imaging device, FIG. 4 is a timing diagram for explaining signal reading when the solid-state imaging device of the present invention is applied to an electronic still camera, and FIG. 5 is a configuration of the electronic still camera. FIG. 6 is a schematic block diagram showing a conventional solid-state imaging device. 10: Light receiving part, 11: Horizontal charge transfer part 12: Output amplifier, 13: Output terminal 14: Photosensitive area, 15: Photosensitive transfer area 18, 19: Transfer electrode, 20: Third electrode 24: Solid-state imaging device R: Red filter, G: Green filter B: Blue filter

Claims (2)

(57) [Claims] 1. A photosensitive area comprising at least a plurality of light receiving elements, and a vertical charge transfer section and a horizontal charge transfer section attached to each vertical column of the light receiving elements, wherein the vertical charge transfer section is provided with a light receiving section. Not only the charge formed by the element can be transferred but also photoelectric conversion can be performed by itself, and a signal of one long wavelength (for example, R) of three primary colors or complementary colors is formed in the vertical charge transfer unit. A solid-state image pickup device, wherein color filters for forming signals of the remaining two colors (for example, G and B) are respectively arranged in the light receiving element. 2. A photosensitive region comprising at least a plurality of light receiving elements, and a vertical charge transfer section and a horizontal charge transfer section attached to each vertical row of the light receiving elements, wherein the vertical charge transfer section is provided with a light receiving element. Not only the charge formed by the element can be transferred but also photoelectric conversion can be performed by itself, and a signal of one long wavelength (for example, R) of three primary colors or complementary colors is formed in the vertical charge transfer unit. Of the signal charges generated by exposing the solid-state imaging device in which the color filters for forming the signals of the remaining two colors (for example, G and B) are respectively arranged in the light receiving element for a predetermined period, the horizontal charge transfer is first performed. The signal charge of the first color formed in the vertical charge transfer section via the transfer section and the signal charge of the second color formed in the light receiving element next are transferred to the vertical charge transfer section to transfer the horizontal charge transfer section. Signal charge of the second color through the section, and then transfer the signal charge of the third color formed in the light receiving element to the vertical charge transfer section, and the signal of the third color through the horizontal charge transfer section. A signal reading method for a solid-state image pickup device, comprising: reading and recording charges in a frame-sequential manner.